High interannual variation in the diet of a tropical forest frugivore (Hylobates lar)

Frugivores must deal with seasonal changes in fruit availability and changes from year to year, as most species of tropical forest fruiting trees have considerable interannual variation in phenology and many are mast fruiters. We quantified seasonal and interannual changes in the fruit diet in a frugivore and important seed disperser, the white-handed gibbon, Hylobates lar, in Thailand. We used 40-day following data during April and May replicated in six consecutive years to study interannual variability in the diet, and compared it with seasonal changes measured in monthly samples of the same size collected in three successive years. The 40-day periods of following also allowed us to measure the decline in dietary similarity with time over a finer scale. We measured fruit diet similarity between replicated 5-day periods using the percentage overlap (Renkonen’s) index, and Jaccard’s similarity index. Seasonally, average dietary overlap between adjacent months was low, and similarity app...